LOS ANGELES--The differences between Vista and Windows 7 are subtle--sometimes so subtle that they can go unnoticed.

This point was exacerbated by the fact that the build that developers were given a chance to take home last week doesn't have the new taskbar that represents the most visual difference between Windows 7 and today's Vista desktop.

Microsoft went to the trouble of shifting all the computer kiosks at the Professional Developers Conference over to Windows 7 on Tuesday. But because the version lacked some of the key visual features, some attendees didn't even notice they were running the newer Windows.

But Microsoft felt that keeping the user interface features out of the developer build was critical to keeping the features a surprise at the conference. The company's earlier M1, M2, and M3 builds all leaked out, said Chaitanya Sareen, a program manager in the Windows unit.

As the conference was winding down on Thursday, Sareen and another program manager--Rebecca Deutsch--offered an in-depth look at the changes Microsoft made to the desktop as well as the rationale for them. To get the best understanding of the changes, check out the two embedded videos (apologies for the lack of tripod).

The new taskbar is, in many ways, more akin to Mac OS X's dock than it is to what most Windows users have seen at the bottom of their screens for years.

With Vista and all its recent predecessors, there are a host of different icons at the bottom of the screen, with one group representing favorite items, another representing open program windows and a third representing notifications and items that launch at start-up.

Window 7 aims to do away with most of that redundancy in favor of one collection of large icons that live at the bottom of the screen. The icons represent applications chosen by the user and live there whether an application is running or not.

The large icons serve several purposes. The icon can, of course, be used simply to switch to or launch an application. It is also home to what is known as a "jumplist," sort of like a mini start menu for each program that can contain a series of actions, a link to recent documents, or even a series of controls that let a user take an action without switching to the program itself.

"This is the one button to rule them all," Sareen said. A left click opens the windows while a right click or the swipe of a finger on a touch-sensitive machine brings up the jumplist.

When a program is open, the icon also allows a user to preview that application's open windows. Clicking on a thumbnail naturally brings that window to the front. Hovering over the preview, though, temporarily previews that window as if it were in front, but doesn't actually complete the change--a feature Microsoft is calling "Aero Peek."

The idea came as the company tried to solve a riddle: what was the perfect size for a thumbnail window? For things like graphical Web pages or a pair of photos, a small representation might do the trick. But when one is trying to, say, flip between two similar Word documents or e-mails, it gets harder.

"The perfect size of the thumbnail is the actual size of the window," Sareen said. And that's how Aero Peek was born.

The goal with that feature and others, Sareen said, is to find ways to remove some of the things that make computing harder, what he calls "paper cuts." They aren't bugs, so much as things that are needlessly complicated or nonintuitive.

"We kind of went on a war against paper cuts," he said.

The company is also trying to reduce all of those annoying notifications that pop up along the right hand side of the computer. Developers can still write code that makes them appear, Deutsch said, but with each one that pops up, users have the option of disabling all such warnings from that program. The idea is to use social engineering to convince developers to bother the user far less often.